The present invention relates generally to the field of magnetic data storage and retrieval. In particular, the present invention relates to a thin-film transducing head having a two-piece shared pole design to reduce thermal pole tip protrusion.
In a magnetic data storage and retrieval system, a thin-film transducing head typically includes a transducer, a substrate upon which the transducer is built, and an overcoat deposited over the transducer. The transducer generally consists of two portions, a writer portion for storing magnetically-encoded information on a magnetic disc and a reader portion for retrieving that magnetically-encoded information from the disc. The reader portion typically consists of a bottom shield, a top shield, and a magnetoresistive (MR) sensor positioned between the bottom and top shields. Magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. The change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary.
The writer portion typically consists of a top and bottom pole, which are separated from each other at the air bearing surface of the writer by a gap layer and which are connected to each other at a region distal from the air bearing surface by a back via, or write via. The air bearing surface is the surface of the recording head immediately adjacent the magnetic media or disc. Positioned between the top and bottom poles are one or more layers of conductive coils encapsulated by insulating layers. The writer portion and the reader portion are often arranged in a merged-configuration in which a shared pole serves as both the top shield in the reader portion and the bottom pole in the writer portion.
To write data to the magnetic media, an electrical current is caused to flow through the conductive coils to thereby induce a magnetic field across the write gap, between the top and bottom poles. By reversing the polarity of the current through the coils, the polarity of the data written to the magnetic media is also reversed. Because the top pole is generally the trailing pole of the top and bottom poles, the top pole is used to physically write the data to the magnetic media. Accordingly, it is the top pole that defines the track width of the written data. More specifically, the track width is defined by the width of the top pole at the air bearing surface.
The layers of the transducer, which include both metallic and insulating layers, all have differing mechanical and chemical properties from the substrate. These different properties affect several aspects of the transducer performance. First the layers of the transducing head will be lapped at different rates. Thus, when an air bearing surface (ABS) of the transducing head is lapped during its fabrication, different amounts of the layers will be removed, resulting in the transducing head having an uneven ABS. Commonly, a greater amount of the metallic layers of the transducer will be removed during the lapping process than will be removed from the substrate. Thus, this lapping process results in a pole tip recession (PTR) of the metallic layers of the transducer with respect to the substrate. The PTR of a particular layer is defined as the distance between the air bearing surface of the substrate and the air bearing surface of that layer.
Another difference in the properties of the substrate and the transducer layers occurs as the magnetic data storage and retrieval system is operated. During operation, the transducing head is subjected to increasing temperatures within the magnetic data storage and retrieval system. In addition, a temperature of the transducing head itself, or a part thereof, may be significantly higher than the temperature within the magnetic data storage and retrieval system due to heat dissipation caused by electrical currents in the transducer. The coefficient of thermal expansion (CTE) of materials used in forming the substrate is typically much smaller than the CTE of the materials used in forming the metallic layers of the transducer. Due to the larger CTE of the transducer""s metallic layers, those layers will tend to expand a greater amount in response to higher temperatures than the substrate. Thus, when the transducing head is subjected to high operating temperatures, the metallic layers normally protrude closer to the disc than the substrate, thereby affecting the PTR of the transducer. This change in PTR caused by temperatures is referred to as the Thermal PTR (TPTR).
During operation of the magnetic data storage and retrieval system, the transducing head is positioned in close proximity to the magnetic media. The distance between the transducer and the media is preferably small enough to allow for writing to and reading from magnetic media with a large areal density and great enough to prevent contact between the magnetic media and the transducer. Performance of the transducer depends primarily on this distance.
To keep the distance between the transducing head and the magnetic media constant, PTR should not change significantly with temperature. If TPTR is large, then the spacing between the transducer and the media will change significantly with temperature, thereby requiring the low-temperature fly height to be high enough to accommodate this variation at higher operating temperatures. On the other hand, if TPTR is close to zero, the low-temperature fly height can be reduced.
As areal density of the magnetic media increases, the requirements for transducing head fly height become such that TPTR takes up a significant portion of the head disc spacing. Much of the TPTR originates from the top and bottom shields, which constitute much of the metal exposed at the ABS. The mismatched CTE between the materials of the transducing head, in particular the shields, and the material of the substrate give rise to the PTR. One method to reduce this effect is to reduce the volume of the shields photolithographically. This is relatively a simple matter where the bottom shield is concerned, however, for heads featuring a shared pole, or top shield and bottom pole which are defined during the same photo step, there is a fundamental limitation in that the structure has to be long enough to reach the writer via and thereby complete the magnetic circuit to the top pole.
The present invention is a transducing head structure that reduces the TPTR when the transducing head is operated at high temperatures and also maintains a complete magnetic circuit between the bottom pole and the top pole.
The present invention relates to a data transducer having an air bearing surface. The data transducer includes a write via and a top pole having one end adjacent the air bearing surface and an opposite end contacting the write via. A yoke extends from the write via in two directions towards the air bearing surface and is recessed from the air bearing surface. The yoke has a first end and a second end. A shared pole is located adjacent the air bearing surface and co-planar to the yoke wherein a gap is located between the shared pole and the yoke. A shared pole extension extends between the shared pole and the first and second ends of the yoke.